1. Field of the Invention
The present invention relates to a washing machine, and more particularly to a spin-dry control method in a washing machine which is capable of enhancing the accuracy of sensing the amount of clothes contained in the washing machine, and an unbalance of the clothes, thereby achieving an optimal spin-dry operation.
2. Description of the Related Art
Generally, a washing machine is an appliance adapted to remove contaminants attached to clothes by utilizing actions of detergent and water. The recent trend of such a washing machine is to sense the amount of clothes contained in the washing machine to perform wash, rinse, spin-dry, and dry cycles in accordance with a wash water level, wash time, amount of detergent, and water flows for rinse and wash cycles determined based on the sensed clothes amount.
FIG. 1 is a sectional view illustrating an inner configuration of a general washing machine.
As shown in FIG. 1, the washing machine includes a casing 2, a water tub 10 mounted in the casing 2, and adapted to contain wash water w therein, a wash tub 20 rotatably mounted in the water tub 10, and adapted to contain clothes m, to be washed, therein, and a motor 30 adapted to support the wash tub 20 while rotating the wash tub 20.
The casing 2 is provided, at one wall thereof, with a clothes loading/unloading opening 2a. A door 4 is also hingably mounted to the wall of the casing 2 to open and close the clothes loading/unloading opening 2a. 
The door 4 includes a door frame 5 hingably coupled to the casing 2, and a door glass 6 mounted to the door frame 5.
The wash tub 20 is provided with a clothes loading/unloading opening 21 for allowing the user to load clothes m into the wash tub 20 and to unload the loaded clothes m from the wash tub 20. The wash tub 20 is also provided with water holes 22, through which wash water w is introduced into and discharged from the wash tub 20.
The motor 30 includes a rotating shaft 32 extending through the water tub 10 while being supported by a bearing 34 mounted to the water tub 10. The rotating shaft 32 is connected to the wash tub 20 at an end thereof spaced away from the motor 30. A Hall sensor is also provided at the motor 30 to measure an RPM or rotated angle of the motor 30.
The washing machine also includes a water supply unit for supplying wash water w fed from the outside of the washing machine into the water tub 10. The water supply unit includes a water supply valve 42 connected to an external hose 41, and adapted to control supply of clean water through the external hose 41, and a detergent box 43 provided with a water supply passage, a detergent storing space, and an outlet to discharge water supplied into the washing machine in a state of being mixed with detergent stored therein.
The washing machine further includes a drainage unit for externally draining wash water w contained in the water tub 10. The drainage unit includes a drainage hose 45 connected to the water tub 10, and a drainage pump 46 for pumping wash water w from the water tub 10 through the drainage hose 45. The drainage hose 45 may have the form of a bellows tube. In some cases, the drainage pump 46 may be dispensed with. In this case, a drainage valve may be installed in the drainage hose 45 to control drainage of wash water w through the drainage hose 45.
The washing machine also includes a control unit 49 for controlling the motor 30, water supply valve 42, and drainage pump 46 in accordance with an operation of the user or a sensed clothes amount.
Now, operation of the conventional washing machine having the above mentioned configuration will be described.
When the washing machine is operated under the condition in which the door 4 has been closed after clothes m have been loaded in the wash tub 20, the control unit 49 senses the amount of the loaded clothes m, and then sets a desired wash water level, a desired wash time, a desired amount of detergent, and desired water flows for rinse and wash cycles, based on the sensed clothes amount.
Thereafter, the control unit 49 controls the water supply valve 42 to be opened for a time set in accordance with the sensed clothes amount, thereby supplying wash water w into the washing machine until the supplied wash water w reaches the set wash water level. The supplied wash water w is fed into the water tub 10, so that it is contained in the water tub 10. The control unit 49 then drives the motor 30 to rotate the wash tub 20 at a predetermined RPM for a predetermined time. Thus, the clothes m contained in the wash tub 20 are washed in accordance with action of the wash water w. That is, stains are removed from the clothes m. After completion of this wash cycle, the wash water existing in the water tub 10 in a contaminated state is externally drained from the washing machine through the drainage unit.
Subsequently, the washing machine performs, several times, a rinse cycle for rinsing the washed clothes m to remove bubbles remaining on the clothes m. This rinse cycle is carried out under the condition in which the water supply valve 42 and motor 30 are controlled, based on the sensed clothes amount, as in the wash cycle. The contaminated water containing the removed bubbles is externally drained from the washing machine through the drainage unit.
After performing the rinse cycle several times, the washing machine performs a spin-dry cycle for centrifugally removing moisture form the clothes m.
The spin-dry cycle includes a clothes amount sensing process for sensing the amount of clothes, to be spin-dried, to determine an optimal spin-dry or an optical spin-dry RPM, and an unbalance sensing process for sensing an unbalance of the clothes to determine whether a main spin-dry process or a clothes disentangling process is to be carried out. The spin-dry cycle also includes the main spin-dry process, which is carried out following the clothes amount sensing process or unbalance sensing process, to control the motor to rotate at high speed, thereby spin-drying the clothes.
FIG. 2 is a flow chart illustrating a conventional spin-dry control method in the above mentioned conventional washing machine. FIG. 3 is a graph depicting a variation in the RPM of the motor in the spin-dry cycle carried out in the conventional washing machine in accordance with the conventional spin-dry control method.
In accordance with the conventional spin-dry control method, as shown in FIGS. 2 and 3, when a wash or rinse cycle is completed, or when an independent spin-dry cycle is selected, a spin-dry operation is carried out in the washing machine by performing a clothes amount sensing process two times (Stages a), performing an unbalance sensing process at least one time (Stage b), and then performing a main spin-dry process (Stage d).
In the clothes amount sensing process (Stage a), the motor 30 is first started up, and is then accelerated until the RPM thereof reaches a first predetermined RPM rpm1. When the RPM of the motor 30 reaches the first predetermined RPM rpm1, the motor 30 is driven in a constant speed state to constantly rotate at the first predetermined RPM rpm1. After the constant speed state of the motor 30 is continued for a predetermined time, the motor 30 is turned off. Meanwhile, a variation in pulse width modulation (PWM) duty value occurring in a duration from the start-up state to the constant speed state of the motor 30 is measured. Also, a rotated angle of the motor 30 caused by a surplus rotation of the motor 30 following the turning-off thereof is also measured. Based on the measured PWM duty value variation and the measured surplus rotation angle, the amount of the clothes is sensed at each of the stages a (Steps S1 and S2).
Thereafter, a mean value of the clothes amounts respectively sensed in the clothes amount sensing process carried out two times (Stages a) is derived. The derived mean clothes amount value is then determined as a final clothes amount (Step S3).
In the unbalance sensing process (Stage b), the motor 30 is accelerated until the RPM thereof reaches a second predetermined RPM rpm2 higher than the first predetermined RPM rpm1. When the RPM of the motor 30 reaches the second predetermined RPM rpm2, the motor 30 is driven in a constant speed state to rotate constantly at the second predetermined RPM rpm2. After the constant speed state of the motor 30 is continued for a predetermined time, the motor 30 is turned off. Meanwhile, an RPM ripple generated during the constant speed duration is measured. Based on the measured RPM ripple, a clothes unbalance is sensed (Step S4).
When it is determined that the clothes unbalance sensed in the unbalance sensing process (Stage b) is not less than a predetermined unbalance value, the washing machine performs a clothes disentangling process to remove the clothes unbalance (Stage c), and then again performs the unbalance sensing process (Stage b′) (Steps S5 and S6).
On the other hand, when it is determined that the clothes unbalance sensed after the clothes disentangling process (Stage c) is less than the predetermined unbalance value, the motor 30 is driven at an RPM rpm3 (rpm3>rpm2) determined based on the final clothes amount, for a predetermined time determined based on the final clothes amount, thereby causing the clothes to be spin-dried at high speed (Step S7).
In accordance with the conventional spin-dry control method, however, it is impossible to obtain an optimal spin-dry result because the clothes amount sensing process for sensing a spin-dry load is carried out only at an initial stage of the spin-dry cycle (Stages a), so that there may be a difference between the actual clothes amount and the sensed clothes amount caused by removal of moisture from the clothes or other variations in spin-dry parameters occurring with the passage of time. Furthermore, the calculated clothes amount may be different from the actual clothes amount in that it may be overestimated due to a possible clothes unbalance. In addition, the sensed clothes amount may have a considerable error because the number of clothes amount sensing times (Stages a) is only two.
Meanwhile, the RPM ripple of the washing machine is influenced by the amount of clothes as well as the unbalance of clothes. In order to more accurately sense the clothes unbalance, accordingly, it is necessary to carry out the sensing of the clothes unbalance, based on the RPM ripple and clothes amount.
Where the sensing of the clothes unbalance (Stage b) is again performed, following a clothes disentangling process (Stage c) or two clothes amount sensing processes (Stages a) carried out for removal of clothes unbalance, the amount of the clothes is more or less reduced due to a spin-dry effect generated during the clothes disentangling process (Stage c) or the unbalance sensing process (Stage b). For this reason, where the sensing of the clothes unbalance is carried out, based on only the RPM ripple, as mentioned above, the measured RPM ripple may be greater than an actual RPM ripple. In this case, there may be an increased possibility that entrance to the main spin-dry process fails.